Although considered as an air pollutant, nitrogen monoxide (NO) was reported to be a physiological active substance that plays a very important role in promoting vasodilation and blood circulation in the humane cardiovascular system. Prof. Louis Ignarro was awarded the 1998 Nobel Prize for his work to demonstrate the discovery. Since then, it has been revealed that nitrogen monoxide has a connection to various physiological phenomena and diseases in the neurotransmission system which controls learning, memory and pain alleviation, and the cardiovascular and immune systems.
As well known, the nitrogen monoxide (NO) production in human body takes place as three types of nitrogen monoxide synthases convert L-arginine to L-citrulline. Nitrogen monoxide (NO), which is produced at level of several nanomoles in the cardiovascular and nervous systems and at level of several micromoles in macrophages playing an important role in relation to the immune system, eliminates the infecting bacteria or viruses in human body.
Determining the production time, amount and distribution of nitrogen monoxide production in human body gives decisive clues to the numerous physiological mechanisms in which nitrogen monoxide participates, and thus many institutions have been studying on the measurement of nitrogen monoxide. However, the accurate concentration of nitrogen monoxide is hard to determine because nitrogen monoxide molecules are such a tiny substance about 30 dalton in molecular weight and reactive radicals which can freely diffuse through a cell membrane. The conventional methods for determining the concentration of nitrogen monoxide include an electrochemical method based on the oxidation-reduction reaction, a method of measuring photoluminescence pertaining to chemical reactions, or the like. Among these methods, the nitrogen monoxide measurement method using the electrochemical technique has been employed in many research institutions to determine the concentration of nitrogen monoxides. However, the measurement result in regard to the amount of nitrogen monoxide in a same portion of human body varies ranging from several hundred nanomoles to several dozens of micromoles, depending on the research institutions. This problem regarding selectivity occurs because different kinds of physiological active substances, such as dopamine, tyrosine, 5-hydroxytriptamine (5-HT), or the like, participate in the oxidation-reduction reactions in human body. To solve this problem, a polymer such as nafion is applied onto the outer surface of electrodes to enhance the selectivity to nitrogen monoxide. However, the thickness and the number of the polymer coatings may significantly affect the measurement results. On the other hand, the method of measuring photoluminescence pertaining to chemical reactions is the most success as a method commercially available to measure nitrogen monoxide, with a limitation as an indirect measurement method closely affected by the production amount of N2O3, reaction conditions, or the like. Instead of measuring nitrogen monoxide produced in human body, the method is to measure the amount of fluorescent dye produced when a nitrogen compound (N2O3) formed from nitrogen monoxide and oxygen reacts with the reaction precursor of an organic dye. Thus there is a demand for developing a sensor to accurately determine an infinitesimal concentration of nitrogen monoxide.
According to the research results obtained by the inventors of the present invention, it is possible to detect an infinitesimal amount of nitrogen monoxide by using a nanohybrid structure that includes semiconducting quantum dot nano-particles combined with a molecule recognizer selectively forming a bonding to nitrogen monoxide, thereby completing the present invention.